Computer hard drives remain a low speed component for data storage in computer systems. While the computational power of processing units (i.e., CPUs) and the capacity of memory and external storage of computer systems have been increased consistent with Moore's law for many years, access latency and data transmission rate of hard drives have not kept up with this pace. This is largely due to the mechanical nature of the rotating disks and moving heads. For example, to perform a read operation, traditional hard drives utilize an electrically or magnetically driven mechanical actuator assembly to first move a read-write head attached to the actuator assembly to a desired track on the hard disk, which is a concentric circular strip. Next, the read-write head waits for a desired sector of the track to rotate and arrive under the head. The data stored on the platter then can be read by the read-write head and transmitted by the disk drive. As a result, it takes a long time to access the data.
Recently emerged solid state drives (SSD) do not have moving parts, making it faster than traditional hard drives. However, SSDs use electrically programmable non-volatile flash memory other than magnetic mediums to store data, and thus are significantly more expensive than hard drives. For example, currently a typical 4 TB hard disk drive is priced between $100 and $125, while a 500 GB SSD costs more than that. Moreover, the capacity ratio between HDDs and SSDs can be as high as 800:1.
FIG. 1 is an illustrative diagram showing a conventional disk drive of the prior art. Hard disk 100 includes one or more rotatable disk platters 102 (showing only one in FIG. 1), an actuator assembly 104, a read-write header 106 attached to the actuator assembly 104, multiple tracks on the disk platters, including the outermost track 108 and the innermost track 110, and a central spindle 112 driven by an electric motor that rotates the disk platters around the axis of the spindle.
Actuator assembly 104 is a highly precise moving component in disk drives and requires many sophisticated technologies. It must be able to move accurately, quickly and smoothly. To achieve this, actuator assembly 104 includes several components not shown in FIG. 1 for it to work and meet various requirements, such as, an actuator magnet, a voice coil that drives the actuator arm under a magnetic force induced by the actuator magnet when a current flows through the voice coil, a voice coil motor driver or controller that controls the movement of the voice coil driving the actuator arm and can be very power consumptive, to name a few. Clearly, eliminating the needs for an actuator assembly in disk drives would be advantageous.
To perform a read operation by the disk drive in FIG. 1, read-write head 106 first needs to be moved to the particular track where the data to be read is located. Actuator assembly 104 is rotatable around the axis 105 so that read-write head 106 can move to any track on platter 102. Thus, in actual operation, actuator assembly 104 will rotate back and forth around axis 105, so that read-write head 106 can read from and write data to all tracks on platter 102. In worst case, read-write head 106 may have to move from outermost track 108 to innermost track 110 before read-write head 106 can perform read-write operations. The time needed for actuator assembly 104 to drive read-write head 106 to travel to the desired track, called seek time, ranges from about 4 ms to 15 ms.
After read-write head 106 moves to the desired track, the head has to wait for a particular sector of the track to reach read-write head 106 before any read or write operation can begin. This latency depends on how far the particular sector is away from read-write head 106 when read-write head 106 starts to move to the track and depends on the rotational speed of disk platter 102.